Method and apparatus for direct and interactive ray tracing of a subdivision surface

ABSTRACT

An apparatus and method are described for ray tracing. In particular, one embodiment of an apparatus for ray tracing comprises: feature adaptive subdivision logic to analyze faces on a subdivision surface and to responsively identify the faces as being of a first type or a second type, the feature adaptive subdivision logic to employ a first set of processing techniques to faces of the first type to generate a first patch type and to employ a second set of processing techniques to faces of the second type to generate a second patch type; and ray intersection determination logic to determine an intersection point between a ray and each of the patches of the first patch type and the second patch type.

BACKGROUND

Field of the Invention

This invention relates generally to the field of computer processors.More particularly, the invention relates to an apparatus and method fordirect and interactive ray tracing of a subdivision surface.

Description of the Related Art

Subdivision surface is widely adopted in the digital content creation(DCC) industry because it is smooth, it supports arbitrary topology, andit can be deformed efficiently. Briefly, subdivision surface techniquesare used to represent a smooth surface through the specification of acoarser polygon mesh. The smooth surface may be calculated from thecoarse polygon mesh using a recursive process of subdividing eachpolygonal face into smaller faces that more accurately approximate thesmooth surface.

In rasterization-based rendering systems (e.g., REYES or RendersEverything You Ever Saw), the subdivision surface is usually tessellatedinto triangles, and the triangles are immediately rasterized into aframe buffer. The tessellated mesh does not need be in memory afterrasterization. In contrast, in ray tracing-based rendering systems(e.g., MCRT or Monte Carlo Ray Tracing), the entire tessellated meshneeds to be in memory before rendering is done since a ray may hit themesh in any direction at any time. Consequently, for a productionrenderer using ray tracing, the memory required for the tessellatedmeshes can easily exceed the capacity of modern computer systems.

Tessellation is usually done in the camera space so that surfaces whichare close to the camera should be finely tessellated, and surfaces whichare far away from the camera should be coarsely tessellated.View-dependent tessellation means that tessellation needs be done everytime the camera moves, even though the subdivision surface does notchange. For a ray tracing system, this also leads to rebuilding thebounding volume hierarchy (BVH).

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained from thefollowing detailed description in conjunction with the followingdrawings, in which:

FIG. 1 is a block diagram of an embodiment of a computer system with aprocessor having one or more processor cores and graphics processors;

FIG. 2 is a block diagram of one embodiment of a processor having one ormore processor cores, an integrated memory controller, and an integratedgraphics processor;

FIG. 3 is a block diagram of one embodiment of a graphics processorwhich may be a discreet graphics processing unit, or may be graphicsprocessor integrated with a plurality of processing cores;

FIG. 4 is a block diagram of an embodiment of a graphics-processingengine for a graphics processor;

FIG. 5 is a block diagram of another embodiment of a graphics processor;

FIG. 6 is a block diagram of thread execution logic including an arrayof processing elements;

FIG. 7 illustrates a graphics processor execution unit instructionformat according to an embodiment;

FIG. 8 is a block diagram of another embodiment of a graphics processorwhich includes a graphics pipeline, a media pipeline, a display engine,thread execution logic, and a render output pipeline;

FIG. 9A is a block diagram illustrating a graphics processor commandformat according to an embodiment;

FIG. 9B is a block diagram illustrating a graphics processor commandsequence according to an embodiment;

FIG. 10 illustrates exemplary graphics software architecture for a dataprocessing system according to an embodiment;

FIG. 11 illustrates an exemplary IP core development system that may beused to manufacture an integrated circuit to perform operationsaccording to an embodiment;

FIG. 12 illustrates an exemplary system on a chip integrated circuitthat may be fabricated using one or more IP cores, according to anembodiment;

FIG. 13 illustrates an exemplary graphics processor architecture whichincludes ray tracing logic and circuitry within a rendering engine forimplementing one embodiment of the invention;

FIG. 14 illustrates an exemplary ring defined around a set of controlvertices;

FIGS. 15A-B illustrate the projection of a Bezier surface including asurface and a ray in three-dimensional space (15A) and a correspondingprojected surface (15B);

FIG. 16 illustrates an exemplary Gregory patch having 20 controlvertices; and

FIG. 17 illustrates a method for performing ray tracing in accordancewith one embodiment of the invention.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the embodiments of the invention described below. Itwill be apparent, however, to one skilled in the art that theembodiments of the invention may be practiced without some of thesespecific details. In other instances, well-known structures and devicesare shown in block diagram form to avoid obscuring the underlyingprinciples of the embodiments of the invention.

Exemplary Graphics Processor Architectures and Data Types

System Overview

FIG. 1 is a block diagram of a processing system 100, according to anembodiment. In various embodiments the system 100 includes one or moreprocessors 102 and one or more graphics processors 108, and may be asingle processor desktop system, a multiprocessor workstation system, ora server system having a large number of processors 102 or processorcores 107. In on embodiment, the system 100 is a processing platformincorporated within a system-on-a-chip (SoC) integrated circuit for usein mobile, handheld, or embedded devices.

An embodiment of system 100 can include, or be incorporated within aserver-based gaming platform, a game console, including a game and mediaconsole, a mobile gaming console, a handheld game console, or an onlinegame console. In some embodiments system 100 is a mobile phone, smartphone, tablet computing device or mobile Internet device. Dataprocessing system 100 can also include, couple with, or be integratedwithin a wearable device, such as a smart watch wearable device, smarteyewear device, augmented reality device, or virtual reality device. Insome embodiments, data processing system 100 is a television or set topbox device having one or more processors 102 and a graphical interfacegenerated by one or more graphics processors 108.

In some embodiments, the one or more processors 102 each include one ormore processor cores 107 to process instructions which, when executed,perform operations for system and user software. In some embodiments,each of the one or more processor cores 107 is configured to process aspecific instruction set 109. In some embodiments, instruction set 109may facilitate Complex Instruction Set Computing (CISC), ReducedInstruction Set Computing (RISC), or computing via a Very LongInstruction Word (VLIW). Multiple processor cores 107 may each process adifferent instruction set 109, which may include instructions tofacilitate the emulation of other instruction sets. Processor core 107may also include other processing devices, such a Digital SignalProcessor (DSP).

In some embodiments, the processor 102 includes cache memory 104.Depending on the architecture, the processor 102 can have a singleinternal cache or multiple levels of internal cache. In someembodiments, the cache memory is shared among various components of theprocessor 102. In some embodiments, the processor 102 also uses anexternal cache (e.g., a Level-3 (L3) cache or Last Level Cache (LLC))(not shown), which may be shared among processor cores 107 using knowncache coherency techniques. A register file 106 is additionally includedin processor 102 which may include different types of registers forstoring different types of data (e.g., integer registers, floating pointregisters, status registers, and an instruction pointer register). Someregisters may be general-purpose registers, while other registers may bespecific to the design of the processor 102.

In some embodiments, processor 102 is coupled to a processor bus 110 totransmit communication signals such as address, data, or control signalsbetween processor 102 and other components in system 100. In oneembodiment the system 100 uses an exemplary ‘hub’ system architecture,including a memory controller hub 116 and an Input Output (I/O)controller hub 130. A memory controller hub 116 facilitatescommunication between a memory device and other components of system100, while an I/O Controller Hub (ICH) 130 provides connections to I/Odevices via a local I/O bus. In one embodiment, the logic of the memorycontroller hub 116 is integrated within the processor.

Memory device 120 can be a dynamic random access memory (DRAM) device, astatic random access memory (SRAM) device, flash memory device,phase-change memory device, or some other memory device having suitableperformance to serve as process memory. In one embodiment the memorydevice 120 can operate as system memory for the system 100, to storedata 122 and instructions 121 for use when the one or more processors102 executes an application or process. Memory controller hub 116 alsocouples with an optional external graphics processor 112, which maycommunicate with the one or more graphics processors 108 in processors102 to perform graphics and media operations.

In some embodiments, ICH 130 enables peripherals to connect to memorydevice 120 and processor 102 via a high-speed I/O bus. The I/Operipherals include, but are not limited to, an audio controller 146, afirmware interface 128, a wireless transceiver 126 (e.g., Wi-Fi,Bluetooth), a data storage device 124 (e.g., hard disk drive, flashmemory, etc.), and a legacy I/O controller 140 for coupling legacy(e.g., Personal System 2 (PS/2)) devices to the system. One or moreUniversal Serial Bus (USB) controllers 142 connect input devices, suchas keyboard and mouse 144 combinations. A network controller 134 mayalso couple to ICH 130. In some embodiments, a high-performance networkcontroller (not shown) couples to processor bus 110. It will beappreciated that the system 100 shown is exemplary and not limiting, asother types of data processing systems that are differently configuredmay also be used. For example, the I/O controller hub 130 may beintegrated within the one or more processor 102, or the memorycontroller hub 116 and I/O controller hub 130 may be integrated into adiscreet external graphics processor, such as the external graphicsprocessor 112.

FIG. 2 is a block diagram of an embodiment of a processor 200 having oneor more processor cores 202A-202N, an integrated memory controller 214,and an integrated graphics processor 208. Those elements of FIG. 2having the same reference numbers (or names) as the elements of anyother figure herein can operate or function in any manner similar tothat described elsewhere herein, but are not limited to such. Processor200 can include additional cores up to and including additional core202N represented by the dashed lined boxes. Each of processor cores202A-202N includes one or more internal cache units 204A-204N. In someembodiments each processor core also has access to one or more sharedcached units 206.

The internal cache units 204A-204N and shared cache units 206 representa cache memory hierarchy within the processor 200. The cache memoryhierarchy may include at least one level of instruction and data cachewithin each processor core and one or more levels of shared mid-levelcache, such as a Level 2 (L2), Level 3 (L3), Level 4 (L4), or otherlevels of cache, where the highest level of cache before external memoryis classified as the LLC. In some embodiments, cache coherency logicmaintains coherency between the various cache units 206 and 204A-204N.

In some embodiments, processor 200 may also include a set of one or morebus controller units 216 and a system agent core 210. The one or morebus controller units 216 manage a set of peripheral buses, such as oneor more Peripheral Component Interconnect buses (e.g., PCI, PCIExpress). System agent core 210 provides management functionality forthe various processor components. In some embodiments, system agent core210 includes one or more integrated memory controllers 214 to manageaccess to various external memory devices (not shown).

In some embodiments, one or more of the processor cores 202A-202Ninclude support for simultaneous multi-threading. In such embodiment,the system agent core 210 includes components for coordinating andoperating cores 202A-202N during multi-threaded processing. System agentcore 210 may additionally include a power control unit (PCU), whichincludes logic and components to regulate the power state of processorcores 202A-202N and graphics processor 208.

In some embodiments, processor 200 additionally includes graphicsprocessor 208 to execute graphics processing operations. In someembodiments, the graphics processor 208 couples with the set of sharedcache units 206, and the system agent core 210, including the one ormore integrated memory controllers 214. In some embodiments, a displaycontroller 211 is coupled with the graphics processor 208 to drivegraphics processor output to one or more coupled displays. In someembodiments, display controller 211 may be a separate module coupledwith the graphics processor via at least one interconnect, or may beintegrated within the graphics processor 208 or system agent core 210.

In some embodiments, a ring based interconnect unit 212 is used tocouple the internal components of the processor 200. However, analternative interconnect unit may be used, such as a point-to-pointinterconnect, a switched interconnect, or other techniques, includingtechniques well known in the art. In some embodiments, graphicsprocessor 208 couples with the ring interconnect 212 via an I/O link213.

The exemplary I/O link 213 represents at least one of multiple varietiesof I/O interconnects, including an on package I/O interconnect whichfacilitates communication between various processor components and ahigh-performance embedded memory module 218, such as an eDRAM module. Insome embodiments, each of the processor cores 202-202N and graphicsprocessor 208 use embedded memory modules 218 as a shared Last LevelCache.

In some embodiments, processor cores 202A-202N are homogenous coresexecuting the same instruction set architecture. In another embodiment,processor cores 202A-202N are heterogeneous in terms of instruction setarchitecture (ISA), where one or more of processor cores 202A-N executea first instruction set, while at least one of the other cores executesa subset of the first instruction set or a different instruction set. Inone embodiment processor cores 202A-202N are heterogeneous in terms ofmicroarchitecture, where one or more cores having a relatively higherpower consumption couple with one or more power cores having a lowerpower consumption. Additionally, processor 200 can be implemented on oneor more chips or as an SoC integrated circuit having the illustratedcomponents, in addition to other components.

FIG. 3 is a block diagram of a graphics processor 300, which may be adiscrete graphics processing unit, or may be a graphics processorintegrated with a plurality of processing cores. In some embodiments,the graphics processor communicates via a memory mapped I/O interface toregisters on the graphics processor and with commands placed into theprocessor memory. In some embodiments, graphics processor 300 includes amemory interface 314 to access memory. Memory interface 314 can be aninterface to local memory, one or more internal caches, one or moreshared external caches, and/or to system memory.

In some embodiments, graphics processor 300 also includes a displaycontroller 302 to drive display output data to a display device 320.Display controller 302 includes hardware for one or more overlay planesfor the display and composition of multiple layers of video or userinterface elements. In some embodiments, graphics processor 300 includesa video codec engine 306 to encode, decode, or transcode media to, from,or between one or more media encoding formats, including, but notlimited to Moving Picture Experts Group (MPEG) formats such as MPEG-2,Advanced Video Coding (AVC) formats such as H.264/MPEG-4 AVC, as well asthe Society of Motion Picture & Television Engineers (SMPTE) 421 M/VC-1,and Joint Photographic Experts Group (JPEG) formats such as JPEG, andMotion JPEG (MJPEG) formats.

In some embodiments, graphics processor 300 includes a block imagetransfer (BLIT) engine 304 to perform two-dimensional (2D) rasterizeroperations including, for example, bit-boundary block transfers.However, in one embodiment, 2D graphics operations are performed usingone or more components of graphics-processing engine (GPE) 310. In someembodiments, graphics-processing engine 310 is a compute engine forperforming graphics operations, including three-dimensional (3D)graphics operations and media operations.

In some embodiments, GPE 310 includes a 3D pipeline 312 for performing3D operations, such as rendering three-dimensional images and scenesusing processing functions that act upon 3D primitive shapes (e.g.,rectangle, triangle, etc.). The 3D pipeline 312 includes programmableand fixed function elements that perform various tasks within theelement and/or spawn execution threads to a 3D/Media sub-system 315.While 3D pipeline 312 can be used to perform media operations, anembodiment of GPE 310 also includes a media pipeline 316 that isspecifically used to perform media operations, such as videopost-processing and image enhancement.

In some embodiments, media pipeline 316 includes fixed function orprogrammable logic units to perform one or more specialized mediaoperations, such as video decode acceleration, video de-interlacing, andvideo encode acceleration in place of, or on behalf of video codecengine 306. In some embodiments, media pipeline 316 additionallyincludes a thread spawning unit to spawn threads for execution on3D/Media sub-system 315. The spawned threads perform computations forthe media operations on one or more graphics execution units included in3D/Media sub-system 315.

In some embodiments, 3D/Media subsystem 315 includes logic for executingthreads spawned by 3D pipeline 312 and media pipeline 316. In oneembodiment, the pipelines send thread execution requests to 3D/Mediasubsystem 315, which includes thread dispatch logic for arbitrating anddispatching the various requests to available thread executionresources. The execution resources include an array of graphicsexecution units to process the 3D and media threads. In someembodiments, 3D/Media subsystem 315 includes one or more internal cachesfor thread instructions and data. In some embodiments, the subsystemalso includes shared memory, including registers and addressable memory,to share data between threads and to store output data.

3D/Media Processing

FIG. 4 is a block diagram of a graphics processing engine 410 of agraphics processor in accordance with some embodiments. In oneembodiment, the GPE 410 is a version of the GPE 310 shown in FIG. 3.Elements of FIG. 4 having the same reference numbers (or names) as theelements of any other figure herein can operate or function in anymanner similar to that described elsewhere herein, but are not limitedto such.

In some embodiments, GPE 410 couples with a command streamer 403, whichprovides a command stream to the GPE 3D and media pipelines 412, 416. Insome embodiments, command streamer 403 is coupled to memory, which canbe system memory, or one or more of internal cache memory and sharedcache memory. In some embodiments, command streamer 403 receivescommands from the memory and sends the commands to 3D pipeline 412and/or media pipeline 416. The commands are directives fetched from aring buffer, which stores commands for the 3D and media pipelines 412,416. In one embodiment, the ring buffer can additionally include batchcommand buffers storing batches of multiple commands. The 3D and mediapipelines 412, 416 process the commands by performing operations vialogic within the respective pipelines or by dispatching one or moreexecution threads to an execution unit array 414. In some embodiments,execution unit array 414 is scalable, such that the array includes avariable number of execution units based on the target power andperformance level of GPE 410.

In some embodiments, a sampling engine 430 couples with memory (e.g.,cache memory or system memory) and execution unit array 414. In someembodiments, sampling engine 430 provides a memory access mechanism forexecution unit array 414 that allows execution array 414 to readgraphics and media data from memory. In some embodiments, samplingengine 430 includes logic to perform specialized image samplingoperations for media.

In some embodiments, the specialized media sampling logic in samplingengine 430 includes a de-noise/de-interlace module 432, a motionestimation module 434, and an image scaling and filtering module 436. Insome embodiments, de-noise/de-interlace module 432 includes logic toperform one or more of a de-noise or a de-interlace algorithm on decodedvideo data. The de-interlace logic combines alternating fields ofinterlaced video content into a single fame of video. The de-noise logicreduces or removes data noise from video and image data. In someembodiments, the de-noise logic and de-interlace logic are motionadaptive and use spatial or temporal filtering based on the amount ofmotion detected in the video data. In some embodiments, thede-noise/de-interlace module 432 includes dedicated motion detectionlogic (e.g., within the motion estimation engine 434).

In some embodiments, motion estimation engine 434 provides hardwareacceleration for video operations by performing video accelerationfunctions such as motion vector estimation and prediction on video data.The motion estimation engine determines motion vectors that describe thetransformation of image data between successive video frames. In someembodiments, a graphics processor media codec uses video motionestimation engine 434 to perform operations on video at the macro-blocklevel that may otherwise be too computationally intensive to performwith a general-purpose processor. In some embodiments, motion estimationengine 434 is generally available to graphics processor components toassist with video decode and processing functions that are sensitive oradaptive to the direction or magnitude of the motion within video data.

In some embodiments, image scaling and filtering module 436 performsimage-processing operations to enhance the visual quality of generatedimages and video. In some embodiments, scaling and filtering module 436processes image and video data during the sampling operation beforeproviding the data to execution unit array 414.

In some embodiments, the GPE 410 includes a data port 444, whichprovides an additional mechanism for graphics subsystems to accessmemory. In some embodiments, data port 444 facilitates memory access foroperations including render target writes, constant buffer reads,scratch memory space reads/writes, and media surface accesses. In someembodiments, data port 444 includes cache memory space to cache accessesto memory. The cache memory can be a single data cache or separated intomultiple caches for the multiple subsystems that access memory via thedata port (e.g., a render buffer cache, a constant buffer cache, etc.).In some embodiments, threads executing on an execution unit in executionunit array 414 communicate with the data port by exchanging messages viaa data distribution interconnect that couples each of the sub-systems ofGPE 410.

Execution Units

FIG. 5 is a block diagram of another embodiment of a graphics processor500. Elements of FIG. 5 having the same reference numbers (or names) asthe elements of any other figure herein can operate or function in anymanner similar to that described elsewhere herein, but are not limitedto such.

In some embodiments, graphics processor 500 includes a ring interconnect502, a pipeline front-end 504, a media engine 537, and graphics cores580A-580N. In some embodiments, ring interconnect 502 couples thegraphics processor to other processing units, including other graphicsprocessors or one or more general-purpose processor cores. In someembodiments, the graphics processor is one of many processors integratedwithin a multi-core processing system.

In some embodiments, graphics processor 500 receives batches of commandsvia ring interconnect 502. The incoming commands are interpreted by acommand streamer 503 in the pipeline front-end 504. In some embodiments,graphics processor 500 includes scalable execution logic to perform 3Dgeometry processing and media processing via the graphics core(s)580A-580N. For 3D geometry processing commands, command streamer 503supplies commands to geometry pipeline 536. For at least some mediaprocessing commands, command streamer 503 supplies the commands to avideo front end 534, which couples with a media engine 537. In someembodiments, media engine 537 includes a Video Quality Engine (VQE) 530for video and image post-processing and a multi-format encode/decode(MFX) 533 engine to provide hardware-accelerated media data encode anddecode. In some embodiments, geometry pipeline 536 and media engine 537each generate execution threads for the thread execution resourcesprovided by at least one graphics core 580A.

In some embodiments, graphics processor 500 includes scalable threadexecution resources featuring modular cores 580A-580N (sometimesreferred to as core slices), each having multiple sub-cores 550A-550N,560A-560N (sometimes referred to as core sub-slices). In someembodiments, graphics processor 500 can have any number of graphicscores 580A through 580N. In some embodiments, graphics processor 500includes a graphics core 580A having at least a first sub-core 550A anda second core sub-core 560A. In other embodiments, the graphicsprocessor is a low power processor with a single sub-core (e.g., 550A).In some embodiments, graphics processor 500 includes multiple graphicscores 580A-580N, each including a set of first sub-cores 550A-550N and aset of second sub-cores 560A-560N. Each sub-core in the set of firstsub-cores 550A-550N includes at least a first set of execution units552A-552N and media/texture samplers 554A-554N. Each sub-core in the setof second sub-cores 560A-560N includes at least a second set ofexecution units 562A-562N and samplers 564A-564N. In some embodiments,each sub-core 550A-550N, 560A-560N shares a set of shared resources570A-570N. In some embodiments, the shared resources include sharedcache memory and pixel operation logic. Other shared resources may alsobe included in the various embodiments of the graphics processor.

FIG. 6 illustrates thread execution logic 600 including an array ofprocessing elements employed in some embodiments of a GPE. Elements ofFIG. 6 having the same reference numbers (or names) as the elements ofany other figure herein can operate or function in any manner similar tothat described elsewhere herein, but are not limited to such.

In some embodiments, thread execution logic 600 includes a pixel shader602, a thread dispatcher 604, instruction cache 606, a scalableexecution unit array including a plurality of execution units 608A-608N,a sampler 610, a data cache 612, and a data port 614. In one embodimentthe included components are interconnected via an interconnect fabricthat links to each of the components. In some embodiments, threadexecution logic 600 includes one or more connections to memory, such assystem memory or cache memory, through one or more of instruction cache606, data port 614, sampler 610, and execution unit array 608A-608N. Insome embodiments, each execution unit (e.g. 608A) is an individualvector processor capable of executing multiple simultaneous threads andprocessing multiple data elements in parallel for each thread. In someembodiments, execution unit array 608A-608N includes any numberindividual execution units.

In some embodiments, execution unit array 608A-608N is primarily used toexecute “shader” programs. In some embodiments, the execution units inarray 608A-608N execute an instruction set that includes native supportfor many standard 3D graphics shader instructions, such that shaderprograms from graphics libraries (e.g., Direct 3D and OpenGL) areexecuted with a minimal translation. The execution units support vertexand geometry processing (e.g., vertex programs, geometry programs,vertex shaders), pixel processing (e.g., pixel shaders, fragmentshaders) and general-purpose processing (e.g., compute and mediashaders).

Each execution unit in execution unit array 608A-608N operates on arraysof data elements. The number of data elements is the “execution size,”or the number of channels for the instruction. An execution channel is alogical unit of execution for data element access, masking, and flowcontrol within instructions. The number of channels may be independentof the number of physical Arithmetic Logic Units (ALUs) or FloatingPoint Units (FPUs) for a particular graphics processor. In someembodiments, execution units 608A-608N support integer andfloating-point data types.

The execution unit instruction set includes single instruction multipledata (SIMD) instructions. The various data elements can be stored as apacked data type in a register and the execution unit will process thevarious elements based on the data size of the elements. For example,when operating on a 256-bit wide vector, the 256 bits of the vector arestored in a register and the execution unit operates on the vector asfour separate 64-bit packed data elements (Quad-Word (QW) size dataelements), eight separate 32-bit packed data elements (Double Word (DW)size data elements), sixteen separate 16-bit packed data elements (Word(W) size data elements), or thirty-two separate 8-bit data elements(byte (B) size data elements). However, different vector widths andregister sizes are possible.

One or more internal instruction caches (e.g., 606) are included in thethread execution logic 600 to cache thread instructions for theexecution units. In some embodiments, one or more data caches (e.g.,612) are included to cache thread data during thread execution. In someembodiments, sampler 610 is included to provide texture sampling for 3Doperations and media sampling for media operations. In some embodiments,sampler 610 includes specialized texture or media sampling functionalityto process texture or media data during the sampling process beforeproviding the sampled data to an execution unit.

During execution, the graphics and media pipelines send threadinitiation requests to thread execution logic 600 via thread spawningand dispatch logic. In some embodiments, thread execution logic 600includes a local thread dispatcher 604 that arbitrates thread initiationrequests from the graphics and media pipelines and instantiates therequested threads on one or more execution units 608A-608N. For example,the geometry pipeline (e.g., 536 of FIG. 5) dispatches vertexprocessing, tessellation, or geometry processing threads to threadexecution logic 600 (FIG. 6). In some embodiments, thread dispatcher 604can also process runtime thread spawning requests from the executingshader programs.

Once a group of geometric objects has been processed and rasterized intopixel data, pixel shader 602 is invoked to further compute outputinformation and cause results to be written to output surfaces (e.g.,color buffers, depth buffers, stencil buffers, etc.). In someembodiments, pixel shader 602 calculates the values of the variousvertex attributes that are to be interpolated across the rasterizedobject. In some embodiments, pixel shader 602 then executes anapplication programming interface (API)-supplied pixel shader program.To execute the pixel shader program, pixel shader 602 dispatches threadsto an execution unit (e.g., 608A) via thread dispatcher 604. In someembodiments, pixel shader 602 uses texture sampling logic in sampler 610to access texture data in texture maps stored in memory. Arithmeticoperations on the texture data and the input geometry data compute pixelcolor data for each geometric fragment, or discards one or more pixelsfrom further processing.

In some embodiments, the data port 614 provides a memory accessmechanism for the thread execution logic 600 output processed data tomemory for processing on a graphics processor output pipeline. In someembodiments, the data port 614 includes or couples to one or more cachememories (e.g., data cache 612) to cache data for memory access via thedata port.

FIG. 7 is a block diagram illustrating a graphics processor instructionformats 700 according to some embodiments. In one or more embodiment,the graphics processor execution units support an instruction set havinginstructions in multiple formats. The solid lined boxes illustrate thecomponents that are generally included in an execution unit instruction,while the dashed lines include components that are optional or that areonly included in a sub-set of the instructions. In some embodiments,instruction format 700 described and illustrated are macro-instructions,in that they are instructions supplied to the execution unit, as opposedto micro-operations resulting from instruction decode once theinstruction is processed.

In some embodiments, the graphics processor execution units nativelysupport instructions in a 128-bit format 710. A 64-bit compactedinstruction format 730 is available for some instructions based on theselected instruction, instruction options, and number of operands. Thenative 128-bit format 710 provides access to all instruction options,while some options and operations are restricted in the 64-bit format730. The native instructions available in the 64-bit format 730 vary byembodiment. In some embodiments, the instruction is compacted in partusing a set of index values in an index field 713. The execution unithardware references a set of compaction tables based on the index valuesand uses the compaction table outputs to reconstruct a nativeinstruction in the 128-bit format 710.

For each format, instruction opcode 712 defines the operation that theexecution unit is to perform. The execution units execute eachinstruction in parallel across the multiple data elements of eachoperand. For example, in response to an add instruction the executionunit performs a simultaneous add operation across each color channelrepresenting a texture element or picture element. By default, theexecution unit performs each instruction across all data channels of theoperands. In some embodiments, instruction control field 714 enablescontrol over certain execution options, such as channels selection(e.g., predication) and data channel order (e.g., swizzle). For 128-bitinstructions 710 an exec-size field 716 limits the number of datachannels that will be executed in parallel. In some embodiments,exec-size field 716 is not available for use in the 64-bit compactinstruction format 730.

Some execution unit instructions have up to three operands including twosource operands, src0 722, src1 722, and one destination 718. In someembodiments, the execution units support dual destination instructions,where one of the destinations is implied. Data manipulation instructionscan have a third source operand (e.g., SRC2 724), where the instructionopcode 712 determines the number of source operands. An instruction'slast source operand can be an immediate (e.g., hard-coded) value passedwith the instruction.

In some embodiments, the 128-bit instruction format 710 includes anaccess/address mode information 726 specifying, for example, whetherdirect register addressing mode or indirect register addressing mode isused. When direct register addressing mode is used, the register addressof one or more operands is directly provided by bits in the instruction710.

In some embodiments, the 128-bit instruction format 710 includes anaccess/address mode field 726, which specifies an address mode and/or anaccess mode for the instruction. In one embodiment the access mode todefine a data access alignment for the instruction. Some embodimentssupport access modes including a 16-byte aligned access mode and a1-byte aligned access mode, where the byte alignment of the access modedetermines the access alignment of the instruction operands. Forexample, when in a first mode, the instruction 710 may use byte-alignedaddressing for source and destination operands and when in a secondmode, the instruction 710 may use 16-byte-aligned addressing for allsource and destination operands.

In one embodiment, the address mode portion of the access/address modefield 726 determines whether the instruction is to use direct orindirect addressing. When direct register addressing mode is used bitsin the instruction 710 directly provide the register address of one ormore operands. When indirect register addressing mode is used, theregister address of one or more operands may be computed based on anaddress register value and an address immediate field in theinstruction.

In some embodiments instructions are grouped based on opcode 712bit-fields to simplify Opcode decode 740. For an 8-bit opcode, bits 4,5, and 6 allow the execution unit to determine the type of opcode. Theprecise opcode grouping shown is merely an example. In some embodiments,a move and logic opcode group 742 includes data movement and logicinstructions (e.g., move (mov), compare (cmp)). In some embodiments,move and logic group 742 shares the five most significant bits (MSB),where move (mov) instructions are in the form of 000xxxxb and logicinstructions are in the form of 0001xxxxb. A flow control instructiongroup 744 (e.g., call, jump (jmp)) includes instructions in the form of0010xxxxb (e.g., 0x20). A miscellaneous instruction group 746 includes amix of instructions, including synchronization instructions (e.g., wait,send) in the form of 0011xxxxb (e.g., 0x30). A parallel math instructiongroup 748 includes component-wise arithmetic instructions (e.g., add,multiply (mul)) in the form of 0100xxxxb (e.g., 0x40). The parallel mathgroup 748 performs the arithmetic operations in parallel across datachannels. The vector math group 750 includes arithmetic instructions(e.g., dp4) in the form of 0101xxxxb (e.g., 0x50). The vector math groupperforms arithmetic such as dot product calculations on vector operands.

Graphics Pipeline

FIG. 8 is a block diagram of another embodiment of a graphics processor800. Elements of FIG. 8 having the same reference numbers (or names) asthe elements of any other figure herein can operate or function in anymanner similar to that described elsewhere herein, but are not limitedto such.

In some embodiments, graphics processor 800 includes a graphics pipeline820, a media pipeline 830, a display engine 840, thread execution logic850, and a render output pipeline 870. In some embodiments, graphicsprocessor 800 is a graphics processor within a multi-core processingsystem that includes one or more general purpose processing cores. Thegraphics processor is controlled by register writes to one or morecontrol registers (not shown) or via commands issued to graphicsprocessor 800 via a ring interconnect 802. In some embodiments, ringinterconnect 802 couples graphics processor 800 to other processingcomponents, such as other graphics processors or general-purposeprocessors. Commands from ring interconnect 802 are interpreted by acommand streamer 803, which supplies instructions to individualcomponents of graphics pipeline 820 or media pipeline 830.

In some embodiments, command streamer 803 directs the operation of avertex fetcher 805 that reads vertex data from memory and executesvertex-processing commands provided by command streamer 803. In someembodiments, vertex fetcher 805 provides vertex data to a vertex shader807, which performs coordinate space transformation and lightingoperations to each vertex. In some embodiments, vertex fetcher 805 andvertex shader 807 execute vertex-processing instructions by dispatchingexecution threads to execution units 852A, 852B via a thread dispatcher831.

In some embodiments, execution units 852A, 852B are an array of vectorprocessors having an instruction set for performing graphics and mediaoperations. In some embodiments, execution units 852A, 852B have anattached L1 cache 851 that is specific for each array or shared betweenthe arrays. The cache can be configured as a data cache, an instructioncache, or a single cache that is partitioned to contain data andinstructions in different partitions.

In some embodiments, graphics pipeline 820 includes tessellationcomponents to perform hardware-accelerated tessellation of 3D objects.In some embodiments, a programmable hull shader 811 configures thetessellation operations. A programmable domain shader 817 providesback-end evaluation of tessellation output. A tessellator 813 operatesat the direction of hull shader 811 and contains special purpose logicto generate a set of detailed geometric objects based on a coarsegeometric model that is provided as input to graphics pipeline 820. Insome embodiments, if tessellation is not used, tessellation components811, 813, 817 can be bypassed.

In some embodiments, complete geometric objects can be processed by ageometry shader 819 via one or more threads dispatched to executionunits 852A, 852B, or can proceed directly to the clipper 829. In someembodiments, the geometry shader operates on entire geometric objects,rather than vertices or patches of vertices as in previous stages of thegraphics pipeline. If the tessellation is disabled the geometry shader819 receives input from the vertex shader 807. In some embodiments,geometry shader 819 is programmable by a geometry shader program toperform geometry tessellation if the tessellation units are disabled.

Before rasterization, a clipper 829 processes vertex data. The clipper829 may be a fixed function clipper or a programmable clipper havingclipping and geometry shader functions. In some embodiments, arasterizer/depth 873 in the render output pipeline 870 dispatches pixelshaders to convert the geometric objects into their per pixelrepresentations. In some embodiments, pixel shader logic is included inthread execution logic 850. In some embodiments, an application canbypass the rasterizer 873 and access un-rasterized vertex data via astream out unit 823.

The graphics processor 800 has an interconnect bus, interconnect fabric,or some other interconnect mechanism that allows data and messagepassing amongst the major components of the processor. In someembodiments, execution units 852A, 852B and associated cache(s) 851,texture and media sampler 854, and texture/sampler cache 858interconnect via a data port 856 to perform memory access andcommunicate with render output pipeline components of the processor. Insome embodiments, sampler 854, caches 851, 858 and execution units 852A,852B each have separate memory access paths.

In some embodiments, render output pipeline 870 contains a rasterizerand depth test component 873 that converts vertex-based objects into anassociated pixel-based representation. In some embodiments, therasterizer logic includes a windower/masker unit to perform fixedfunction triangle and line rasterization. An associated render cache 878and depth cache 879 are also available in some embodiments. A pixeloperations component 877 performs pixel-based operations on the data,though in some instances, pixel operations associated with 2D operations(e.g. bit block image transfers with blending) are performed by the 2Dengine 841, or substituted at display time by the display controller 843using overlay display planes. In some embodiments, a shared L3 cache 875is available to all graphics components, allowing the sharing of datawithout the use of main system memory.

In some embodiments, graphics processor media pipeline 830 includes amedia engine 837 and a video front end 834. In some embodiments, videofront end 834 receives pipeline commands from the command streamer 803.In some embodiments, media pipeline 830 includes a separate commandstreamer. In some embodiments, video front-end 834 processes mediacommands before sending the command to the media engine 837. In someembodiments, media engine 337 includes thread spawning functionality tospawn threads for dispatch to thread execution logic 850 via threaddispatcher 831.

In some embodiments, graphics processor 800 includes a display engine840. In some embodiments, display engine 840 is external to processor800 and couples with the graphics processor via the ring interconnect802, or some other interconnect bus or fabric. In some embodiments,display engine 840 includes a 2D engine 841 and a display controller843. In some embodiments, display engine 840 contains special purposelogic capable of operating independently of the 3D pipeline. In someembodiments, display controller 843 couples with a display device (notshown), which may be a system integrated display device, as in a laptopcomputer, or an external display device attached via a display deviceconnector.

In some embodiments, graphics pipeline 820 and media pipeline 830 areconfigurable to perform operations based on multiple graphics and mediaprogramming interfaces and are not specific to any one applicationprogramming interface (API). In some embodiments, driver software forthe graphics processor translates API calls that are specific to aparticular graphics or media library into commands that can be processedby the graphics processor. In some embodiments, support is provided forthe Open Graphics Library (OpenGL) and Open Computing Language (OpenCL)from the Khronos Group, the Direct3D library from the MicrosoftCorporation, or support may be provided to both OpenGL and D3D. Supportmay also be provided for the Open Source Computer Vision Library(OpenCV). A future API with a compatible 3D pipeline would also besupported if a mapping can be made from the pipeline of the future APIto the pipeline of the graphics processor.

Graphics Pipeline Programming

FIG. 9A is a block diagram illustrating a graphics processor commandformat 900 according to some embodiments. FIG. 9B is a block diagramillustrating a graphics processor command sequence 910 according to anembodiment. The solid lined boxes in FIG. 9A illustrate the componentsthat are generally included in a graphics command while the dashed linesinclude components that are optional or that are only included in asub-set of the graphics commands. The exemplary graphics processorcommand format 900 of FIG. 9A includes data fields to identify a targetclient 902 of the command, a command operation code (opcode) 904, andthe relevant data 906 for the command. A sub-opcode 905 and a commandsize 908 are also included in some commands.

In some embodiments, client 902 specifies the client unit of thegraphics device that processes the command data. In some embodiments, agraphics processor command parser examines the client field of eachcommand to condition the further processing of the command and route thecommand data to the appropriate client unit. In some embodiments, thegraphics processor client units include a memory interface unit, arender unit, a 2D unit, a 3D unit, and a media unit. Each client unithas a corresponding processing pipeline that processes the commands.Once the command is received by the client unit, the client unit readsthe opcode 904 and, if present, sub-opcode 905 to determine theoperation to perform. The client unit performs the command usinginformation in data field 906. For some commands an explicit commandsize 908 is expected to specify the size of the command. In someembodiments, the command parser automatically determines the size of atleast some of the commands based on the command opcode. In someembodiments commands are aligned via multiples of a double word.

The flow diagram in FIG. 9B shows an exemplary graphics processorcommand sequence 910. In some embodiments, software or firmware of adata processing system that features an embodiment of a graphicsprocessor uses a version of the command sequence shown to set up,execute, and terminate a set of graphics operations. A sample commandsequence is shown and described for purposes of example only asembodiments are not limited to these specific commands or to thiscommand sequence. Moreover, the commands may be issued as batch ofcommands in a command sequence, such that the graphics processor willprocess the sequence of commands in at least partially concurrence.

In some embodiments, the graphics processor command sequence 910 maybegin with a pipeline flush command 912 to cause any active graphicspipeline to complete the currently pending commands for the pipeline. Insome embodiments, the 3D pipeline 922 and the media pipeline 924 do notoperate concurrently. The pipeline flush is performed to cause theactive graphics pipeline to complete any pending commands. In responseto a pipeline flush, the command parser for the graphics processor willpause command processing until the active drawing engines completepending operations and the relevant read caches are invalidated.Optionally, any data in the render cache that is marked ‘dirty’ can beflushed to memory. In some embodiments, pipeline flush command 912 canbe used for pipeline synchronization or before placing the graphicsprocessor into a low power state.

In some embodiments, a pipeline select command 913 is used when acommand sequence requires the graphics processor to explicitly switchbetween pipelines. In some embodiments, a pipeline select command 913 isrequired only once within an execution context before issuing pipelinecommands unless the context is to issue commands for both pipelines. Insome embodiments, a pipeline flush command is 912 is requiredimmediately before a pipeline switch via the pipeline select command913.

In some embodiments, a pipeline control command 914 configures agraphics pipeline for operation and is used to program the 3D pipeline922 and the media pipeline 924. In some embodiments, pipeline controlcommand 914 configures the pipeline state for the active pipeline. Inone embodiment, the pipeline control command 914 is used for pipelinesynchronization and to clear data from one or more cache memories withinthe active pipeline before processing a batch of commands.

In some embodiments, return buffer state commands 916 are used toconfigure a set of return buffers for the respective pipelines to writedata. Some pipeline operations require the allocation, selection, orconfiguration of one or more return buffers into which the operationswrite intermediate data during processing. In some embodiments, thegraphics processor also uses one or more return buffers to store outputdata and to perform cross thread communication. In some embodiments, thereturn buffer state 916 includes selecting the size and number of returnbuffers to use for a set of pipeline operations.

The remaining commands in the command sequence differ based on theactive pipeline for operations. Based on a pipeline determination 920,the command sequence is tailored to the 3D pipeline 922 beginning withthe 3D pipeline state 930, or the media pipeline 924 beginning at themedia pipeline state 940.

The commands for the 3D pipeline state 930 include 3D state settingcommands for vertex buffer state, vertex element state, constant colorstate, depth buffer state, and other state variables that are to beconfigured before 3D primitive commands are processed. The values ofthese commands are determined at least in part based the particular 3DAPI in use. In some embodiments, 3D pipeline state 930 commands are alsoable to selectively disable or bypass certain pipeline elements if thoseelements will not be used.

In some embodiments, 3D primitive 932 command is used to submit 3Dprimitives to be processed by the 3D pipeline. Commands and associatedparameters that are passed to the graphics processor via the 3Dprimitive 932 command are forwarded to the vertex fetch function in thegraphics pipeline. The vertex fetch function uses the 3D primitive 932command data to generate vertex data structures. The vertex datastructures are stored in one or more return buffers. In someembodiments, 3D primitive 932 command is used to perform vertexoperations on 3D primitives via vertex shaders. To process vertexshaders, 3D pipeline 922 dispatches shader execution threads to graphicsprocessor execution units.

In some embodiments, 3D pipeline 922 is triggered via an execute 934command or event. In some embodiments, a register write triggers commandexecution. In some embodiments execution is triggered via a ‘go’ or‘kick’ command in the command sequence. In one embodiment commandexecution is triggered using a pipeline synchronization command to flushthe command sequence through the graphics pipeline. The 3D pipeline willperform geometry processing for the 3D primitives. Once operations arecomplete, the resulting geometric objects are rasterized and the pixelengine colors the resulting pixels. Additional commands to control pixelshading and pixel back end operations may also be included for thoseoperations.

In some embodiments, the graphics processor command sequence 910 followsthe media pipeline 924 path when performing media operations. Ingeneral, the specific use and manner of programming for the mediapipeline 924 depends on the media or compute operations to be performed.Specific media decode operations may be offloaded to the media pipelineduring media decode. In some embodiments, the media pipeline can also bebypassed and media decode can be performed in whole or in part usingresources provided by one or more general purpose processing cores. Inone embodiment, the media pipeline also includes elements forgeneral-purpose graphics processor unit (GPGPU) operations, where thegraphics processor is used to perform SIMD vector operations usingcomputational shader programs that are not explicitly related to therendering of graphics primitives.

In some embodiments, media pipeline 924 is configured in a similarmanner as the 3D pipeline 922. A set of media pipeline state commands940 are dispatched or placed into in a command queue before the mediaobject commands 942. In some embodiments, media pipeline state commands940 include data to configure the media pipeline elements that will beused to process the media objects. This includes data to configure thevideo decode and video encode logic within the media pipeline, such asencode or decode format. In some embodiments, media pipeline statecommands 940 also support the use one or more pointers to “indirect”state elements that contain a batch of state settings.

In some embodiments, media object commands 942 supply pointers to mediaobjects for processing by the media pipeline. The media objects includememory buffers containing video data to be processed. In someembodiments, all media pipeline states must be valid before issuing amedia object command 942. Once the pipeline state is configured andmedia object commands 942 are queued, the media pipeline 924 istriggered via an execute command 944 or an equivalent execute event(e.g., register write). Output from media pipeline 924 may then be postprocessed by operations provided by the 3D pipeline 922 or the mediapipeline 924. In some embodiments, GPGPU operations are configured andexecuted in a similar manner as media operations.

Graphics Software Architecture

FIG. 10 illustrates exemplary graphics software architecture for a dataprocessing system 1000 according to some embodiments. In someembodiments, software architecture includes a 3D graphics application1010, an operating system 1020, and at least one processor 1030. In someembodiments, processor 1030 includes a graphics processor 1032 and oneor more general-purpose processor core(s) 1034. The graphics application1010 and operating system 1020 each execute in the system memory 1050 ofthe data processing system.

In some embodiments, 3D graphics application 1010 contains one or moreshader programs including shader instructions 1012. The shader languageinstructions may be in a high-level shader language, such as the HighLevel Shader Language (HLSL) or the OpenGL Shader Language (GLSL). Theapplication also includes executable instructions 1014 in a machinelanguage suitable for execution by the general-purpose processor core1034. The application also includes graphics objects 1016 defined byvertex data.

In some embodiments, operating system 1020 is a Microsoft® Windows®operating system from the Microsoft Corporation, a proprietary UNIX-likeoperating system, or an open source UNIX-like operating system using avariant of the Linux kernel. When the Direct3D API is in use, theoperating system 1020 uses a front-end shader compiler 1024 to compileany shader instructions 1012 in HLSL into a lower-level shader language.The compilation may be a just-in-time (JIT) compilation or theapplication can perform shader pre-compilation. In some embodiments,high-level shaders are compiled into low-level shaders during thecompilation of the 3D graphics application 1010.

In some embodiments, user mode graphics driver 1026 contains a back-endshader compiler 1027 to convert the shader instructions 1012 into ahardware specific representation. When the OpenGL API is in use, shaderinstructions 1012 in the GLSL high-level language are passed to a usermode graphics driver 1026 for compilation. In some embodiments, usermode graphics driver 1026 uses operating system kernel mode functions1028 to communicate with a kernel mode graphics driver 1029. In someembodiments, kernel mode graphics driver 1029 communicates with graphicsprocessor 1032 to dispatch commands and instructions.

IP Core Implementations

One or more aspects of at least one embodiment may be implemented byrepresentative code stored on a machine-readable medium which representsand/or defines logic within an integrated circuit such as a processor.For example, the machine-readable medium may include instructions whichrepresent various logic within the processor. When read by a machine,the instructions may cause the machine to fabricate the logic to performthe techniques described herein. Such representations, known as “IPcores,” are reusable units of logic for an integrated circuit that maybe stored on a tangible, machine-readable medium as a hardware modelthat describes the structure of the integrated circuit. The hardwaremodel may be supplied to various customers or manufacturing facilities,which load the hardware model on fabrication machines that manufacturethe integrated circuit. The integrated circuit may be fabricated suchthat the circuit performs operations described in association with anyof the embodiments described herein.

FIG. 11 is a block diagram illustrating an IP core development system1100 that may be used to manufacture an integrated circuit to performoperations according to an embodiment. The IP core development system1100 may be used to generate modular, re-usable designs that can beincorporated into a larger design or used to construct an entireintegrated circuit (e.g., an SOC integrated circuit). A design facility1130 can generate a software simulation 1110 of an IP core design in ahigh level programming language (e.g., C/C++). The software simulation1110 can be used to design, test, and verify the behavior of the IPcore. A register transfer level (RTL) design can then be created orsynthesized from the simulation model 1100. The RTL design 1115 is anabstraction of the behavior of the integrated circuit that models theflow of digital signals between hardware registers, including theassociated logic performed using the modeled digital signals. Inaddition to an RTL design 1115, lower-level designs at the logic levelor transistor level may also be created, designed, or synthesized. Thus,the particular details of the initial design and simulation may vary.

The RTL design 1115 or equivalent may be further synthesized by thedesign facility into a hardware model 1120, which may be in a hardwaredescription language (HDL), or some other representation of physicaldesign data. The HDL may be further simulated or tested to verify the IPcore design. The IP core design can be stored for delivery to a 3^(rd)party fabrication facility 1165 using non-volatile memory 1140 (e.g.,hard disk, flash memory, or any non-volatile storage medium).Alternatively, the IP core design may be transmitted (e.g., via theInternet) over a wired connection 1150 or wireless connection 1160. Thefabrication facility 1165 may then fabricate an integrated circuit thatis based at least in part on the IP core design. The fabricatedintegrated circuit can be configured to perform operations in accordancewith at least one embodiment described herein.

FIG. 12 is a block diagram illustrating an exemplary system on a chipintegrated circuit 1200 that may be fabricated using one or more IPcores, according to an embodiment. The exemplary integrated circuitincludes one or more application processors 1205 (e.g., CPUs), at leastone graphics processor 1210, and may additionally include an imageprocessor 1215 and/or a video processor 1220, any of which may be amodular IP core from the same or multiple different design facilities.The integrated circuit includes peripheral or bus logic including a USBcontroller 1225, UART controller 1230, an SPI/SDIO controller 1235, andan I²S/I²C controller 1240. Additionally, the integrated circuit caninclude a display device 1245 coupled to one or more of ahigh-definition multimedia interface (HDMI) controller 1250 and a mobileindustry processor interface (MIPI) display interface 1255. Storage maybe provided by a flash memory subsystem 1260 including flash memory anda flash memory controller. Memory interface may be provided via a memorycontroller 1265 for access to SDRAM or SRAM memory devices. Someintegrated circuits additionally include an embedded security engine1270.

Additionally, other logic and circuits may be included in the processorof integrated circuit 1200, including additional graphicsprocessors/cores, peripheral interface controllers, or general purposeprocessor cores.

Apparatus and Method for Direct and Interactive Ray Tracing of aSubdivision Surface

The embodiments of the invention described below include improvedtechniques for ray tracing in which rays and the subdivision surface areintersected directly without tessellation. A numerical solver may beused to find the intersection point. In one embodiment, the numericsolver comprises Newton's Method (also known as the Newton-Raphsonmethod) which is a method for finding successively better approximationsto the roots (or zeroes) of a real-valued function. Experiments haveconfirmed that this solution can interactively render the subdivisionsurface in high quality with a smaller memory footprint.

As illustrated in FIG. 13, one embodiment of the invention isimplemented as ray tracing logic/circuitry 1300 within a graphicsrendering engine 1370 with a graphics processor. The ray tracing logic1300 includes feature adaptive subdivision logic 1301 for identifying“regular” and “irregular” faces of the subdivision surface 1305 at eachstage of subdivision. In one embodiment, a face is considered “regular”if it is a quad with all regular vertices, if none of its edges orvertices are tagged as sharp, and if there are no hierarchical editsthat would influence the shape of the limit patch. Regular faces may beused to generate bi-cubic Bezier patches 1306 and irregular faces may beused to generate Gregory patches 1307. Ray intersection determinationlogic 1302 then determines an intersection point between a ray and eachBezier patch 1306 and Gregory patch 1307 (e.g., using Newton's method inone embodiment, as discussed below). The resulting ray intersection data1308 is then used to identify the ray intersection with the patches andshading of the intersection point 1309 is performed prior to rending thefinal graphical image on the display.

A more detailed description of one embodiment of the invention will nowbe provided. It should be noted, however, that the underlying principlesof the invention are not limited to some of these specific details.

As mentioned, feature adaptive subdivision logic 1301 proceeds byidentifying “regular” faces at each stage of subdivision. In oneembodiment, one ring of the control vertices around the regular face isextracted to form a bi-cubic Bezier patch 1306. In the example shown inFIG. 14, for the patch 1400 defined in the shaded domain (defined byvertices 6, 7, 11, and 10) the ring is defined as the vertices aroundthis rectangle—i.e., vertices 1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, and5. In one embodiment, “irregular” faces are refined, and the processrepeats at the next finer level. When the maximum subdivision level isreached, the irregular face is approximated with a Gregory patch 1307.

In one embodiment, the feature adaptive subdivision logic 1301 generatesa list of bi-cubic Bezier patches 1306 and Gregory patches 1307. Most ofthese patches are Bezier patches given that Gregory patches are onlyused for very small isolated areas around irregular faces.

Since there is no analytic solution to find the intersection pointbetween a ray and a Bezier patch/Gregory patch, in one embodimentNewton's method is applied to find the numerical solution. To reduce thecomplexity of Newton's method, the Bezier patch/Gregory patch isprojected from 3D space to 2D space along the ray with the ray passingthrough the origin of the projected 2D coordinate system. FIG. 15Aillustrates a representation of an exemplary patch in 3D space and FIG.15B illustrates a representation of the patch projected into 2D space.With this projection, finding the intersection point may be accomplishedby finding all of the (u, v) pairs such that P(u,v)=0, where 0≦u, v≦1.The Newton iteration can be written as:

$\begin{bmatrix}u_{k + 1} \\v_{k + 1}\end{bmatrix} = {\begin{bmatrix}u_{k} \\v_{k}\end{bmatrix} - {\begin{bmatrix}\frac{\partial{P_{1}\left( {u,v} \right)}}{\partial u} & \frac{\partial{P_{1}\left( {u,v} \right)}}{\partial v} \\\frac{\partial{P_{2}\left( {u,v} \right)}}{\partial u} & \frac{\partial{P_{2}\left( {u,v} \right)}}{\partial v}\end{bmatrix}^{- 1}\begin{bmatrix}{P_{1}\left( {u_{k},v_{k}} \right)} \\{P_{2}\left( {u_{k},v_{k}} \right)}\end{bmatrix}}}$Where (u_(k),v_(k)) is the uv at step k, and (u_(k+1),v_(k+1)) is the uvat next step k+1.

To compute the equation above, the Bezier and Gregory patches need to beevaluated to determine the location and partial derivatives. In oneembodiment, the Bezier patch is evaluated in accordance with thefollowing equations:

${P\left( {u,v} \right)} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$${{\mathbb{d}{P\left( {u,v} \right)}}/{\mathbb{d}u}} = {\left( {0\mspace{14mu} 1\mspace{14mu} 2u\mspace{14mu} 3u^{2}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$${{\mathbb{d}{P\left( {u,v} \right)}}/{\mathbb{d}v}} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}0 \\1 \\{2v} \\{3v^{2}}\end{pmatrix}}}$ ${{where}\mspace{14mu}{Mz}} = {\begin{bmatrix}1 & 0 & 0 & 0 \\{- 3} & 3 & 0 & 0 \\3 & {- 6} & 3 & 0 \\{- 1} & 3 & {- 3} & 1\end{bmatrix}.}$

In one embodiment, the Gregory patch has 20 control vertices labeled asillustrated in FIG. 16. Using this set of control vertices, the Gregorypatch may be defined as:

${P\left( {u,v} \right)} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} G\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$ ${G = \begin{bmatrix}p_{0} & e_{0}^{-} & e_{3}^{+} & p_{3} \\e_{0}^{+} & F_{0} & F_{3} & e_{2}^{-} \\e_{1}^{-} & F_{1} & F_{2} & e_{2}^{+} \\p_{1} & e_{1}^{+} & e_{2}^{-} & p_{2}\end{bmatrix}},{where}$${F_{0} = \frac{{uf}_{0}^{+} + {vf}_{0}^{-}}{u + v}},{F_{1} = \frac{{\left( {1 - u} \right)f_{1}^{-}} + {vf}_{1}^{+}}{1 - u + v}},{F_{2} = \frac{{\left( {1 - u} \right)f_{2}^{+}} + {\left( {1 - v} \right)f_{2}^{-}}}{2 - u - v}},{F_{3} = \frac{{uf}_{3}^{-} + {\left( {1 - v} \right)f_{3}^{+}}}{1 + u - v}},$

Unlike a Bezier patch, control vertex matrix G is different fordifferent uv. However, for a giving uv, G can be computed with theformula above, and then the same method to evaluate the Bezier patch canbe used to evaluate the Gregory patch at that uv.

As a common issue for Newton's method, the initial uv to start with iscritical. An inappropriate initial uv may lead to an incorrectintersection point or no intersection at all. In one embodiment, to helpdetermine an accurate initial uv, a Bezier patch/Gregory patch isrecursively divided into sub-domains until the control mesh for thesub-domain is flat. In one embodiment, a bounding volume hierarchy (BVH)is built for the Bezier patch/Gregory patch. A BVH is a tree structurein which all geometric objects are wrapped in bounding volumes that formthe leaf nodes of the tree. In one embodiment, each non-leaf node of theBVH only saves an oriented bounding box, and each leaf node also savesthe minimum and maximum uv for the sub-domain. When a ray intersectswith a Bezier patch/Gregory patch, the BVH is intersected with the rayto find the intersected leaf node of the BVH, and the middle point ofthe sub-domain of the leaf node is used as the initial uv to applyNewton's method. Tests have shown this method to generate stable andaccurate intersections between rays and Bezier/Gregory patches.

A method in accordance with one embodiment of the invention isillustrated in FIG. 17. The method may be implemented on the graphicsarchitectures described above but is not limited to any specificarchitecture. At 1701, a control mesh is received defining a subdivisionsurface. At 1702, each face of the subdivision surface is analyzed ateach stage of subdivision. At 1703, if a face is determined to be“regular” then at 1704, a ring is extracted around its control verticesto form a bi-cubic Bezier patch. As mentioned, in one embodiment, a faceis considered “regular” if it is a quad with all regular vertices, ifnone of its edges or vertices are tagged as sharp, and if there are nohierarchical edits that would influence the shape of the limit patch. Ifa face is irregular then at 1705, the face is refined at eachsubdivision level. At 1706, at the maximum subdivision level, the faceis approximated with a Gregory patch. In either case, at 1707, anintersection point between the ray and the Bezier/Gregory patch isdetermined using Newton's method (e.g., using the techniques set forthabove).

Using the techniques described herein offers many advantages overexisting tessellation-based solution. First, these techniques result ina significantly smaller memory footprint. To render high quality images,tessellation-based systems need to tessellate subdivision surfaces intovery small polygons. Each vertex of the tessellated polygons usuallyneeds to save multiple channels of data, such as position, normal,texture coordinate, and partial derivatives. However, direct ray andsubdivision surface intersection only needs to save these data on thecontrol mesh. After the numerical solver finds the UV of theintersection point, these data can be easily evaluated for theintersection point.

In addition, using the techniques described herein, there is no overheadwhen the viewpoint is changed during interactive rendering. Fortessellation-based systems, the tessellation metric is usuallyview-dependent. Surfaces close to the viewpoint need dense tessellation,and surfaces far away from the viewpoint need coarse tessellation,leading to different tessellation when the viewpoint is changing.Different tessellation also leads to a BVH rebuild. Direct ray andsubdivision surface intersection as described herein does not have thisoverhead.

Finally, the techniques described herein result in more accurateintersection data. Tessellation is an approximation for the limitsurface of the subdivision surface. After a ray hits a tessellatedpolygon, vertex data of the hit polygon is linearly interpolated tocompute these data for the hit point. This approximation is usuallyacceptable for most cases; however, it may lead to some visualartifacts, such as shadow acne and non-smooth silhouettes. Direct rayand subdivision surface intersection always finds the intersection pointon the limit surface and the result is more accurate than these existingtechniques.

Embodiments of the invention may include various steps, which have beendescribed above. The steps may be embodied in machine-executableinstructions which may be used to cause a general-purpose orspecial-purpose processor to perform the steps. Alternatively, thesesteps may be performed by specific hardware components that containhardwired logic for performing the steps, or by any combination ofprogrammed computer components and custom hardware components.

As described herein, instructions may refer to specific configurationsof hardware such as application specific integrated circuits (ASICs)configured to perform certain operations or having a predeterminedfunctionality or software instructions stored in memory embodied in anon-transitory computer readable medium. Thus, the techniques shown inthe figures can be implemented using code and data stored and executedon one or more electronic devices (e.g., an end station, a networkelement, etc.). Such electronic devices store and communicate(internally and/or with other electronic devices over a network) codeand data using computer machine-readable media, such as non-transitorycomputer machine-readable storage media (e.g., magnetic disks; opticaldisks; random access memory; read only memory; flash memory devices;phase-change memory) and transitory computer machine-readablecommunication media (e.g., electrical, optical, acoustical or other formof propagated signals—such as carrier waves, infrared signals, digitalsignals, etc.). In addition, such electronic devices typically include aset of one or more processors coupled to one or more other components,such as one or more storage devices (non-transitory machine-readablestorage media), user input/output devices (e.g., a keyboard, atouchscreen, and/or a display), and network connections. The coupling ofthe set of processors and other components is typically through one ormore busses and bridges (also termed as bus controllers). The storagedevice and signals carrying the network traffic respectively representone or more machine-readable storage media and machine-readablecommunication media. Thus, the storage device of a given electronicdevice typically stores code and/or data for execution on the set of oneor more processors of that electronic device. Of course, one or moreparts of an embodiment of the invention may be implemented usingdifferent combinations of software, firmware, and/or hardware.Throughout this detailed description, for the purposes of explanation,numerous specific details were set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the invention may be practiced without someof these specific details. In certain instances, well known structuresand functions were not described in elaborate detail in order to avoidobscuring the subject matter of the present invention. Accordingly, thescope and spirit of the invention should be judged in terms of theclaims which follow.

What is claimed is:
 1. An apparatus for performing ray tracingcomprising: feature adaptive subdivision circuitry to analyze faces on asubdivision surface and to responsively identify the faces as being of afirst type or a second type, wherein a face is considered a first typeof face if it is a quad with all regular vertices, if none of its edgesor vertices are tagged as sharp, and if there are no hierarchical editsthat would influence the shape of a limit patch and wherein a face isconsidered to be a second type of face if it does not meet therequirements for being a first type of face; the feature adaptivesubdivision circuitry to employ a first set of processing techniques tofaces of the first type to generate a first patch type and to employ asecond set of processing techniques to faces of the second type togenerate a second patch type; and ray intersection determinationcircuitry to determine an intersection point between a ray and each ofthe patches of the first patch type and the second patch type.
 2. Theapparatus as in claim 1 wherein the first patch type comprises abi-cubic Bezier patch.
 3. The apparatus as in claim 2 wherein a face ofthe first type includes a set of control vertices and wherein the firstset of processing techniques comprise extracting one ring of the controlvertices around the face to form the bi-cubic Bezier patch.
 4. Theapparatus as in claim 2 wherein the second patch type comprises aGregory patch.
 5. The apparatus as in claim 4 wherein the second set ofprocessing techniques for faces of the second type comprise iterativelyrefining the faces at each finer subdivision level, wherein when amaximum subdivision level is reached, a irregular face is approximatedwith the Gregory patch.
 6. The apparatus as in claim 1 wherein the rayintersection determination circuitry determines the intersection pointbetween a ray and each of the patches of the first patch type and thesecond patch type using Newton's method.
 7. The apparatus as in claim 6wherein to reduce the complexity of Newton's method, each patch of thefirst patch type and the second patch type are projected fromthree-dimensional space to two-dimensional space along the ray, with theray passing through an origin of the two-dimensional projection.
 8. Theapparatus as in claim 7 wherein finding the intersection point using thetwo-dimensional projection is accomplished by finding all of the (u, v)pairs such that P(u,v)=0, where 0≦u, v≦1 and where a Newton iterationcomprises: $\begin{bmatrix}u_{k + 1} \\v_{k + 1}\end{bmatrix} = {\begin{bmatrix}u_{k} \\v_{k}\end{bmatrix} - {\begin{bmatrix}\frac{\partial{P_{1}\left( {u,v} \right)}}{\partial u} & \frac{\partial{P_{1}\left( {u,v} \right)}}{\partial v} \\\frac{\partial{P_{2}\left( {u,v} \right)}}{\partial u} & \frac{\partial{P_{2}\left( {u,v} \right)}}{\partial v}\end{bmatrix}^{- 1}\begin{bmatrix}{P_{1}\left( {u_{k},v_{k}} \right)} \\{P_{2}\left( {u_{k},v_{k}} \right)}\end{bmatrix}}}$ where (u_(k),v_(k)) is the uv at step k, and(u_(k+1),v_(k+1)) is the uv at next step k+1.
 9. The apparatus as inclaim 8 wherein the first patch type comprises a Bezier patch andwherein the Bezier patch is evaluated in accordance with the followingequations:${P\left( {u,v} \right)} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$${{\mathbb{d}{P\left( {u,v} \right)}}/{\mathbb{d}u}} = {\left( {0\mspace{14mu} 1\mspace{14mu} 2u\mspace{14mu} 3u^{2}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$${{\mathbb{d}{P\left( {u,v} \right)}}/{\mathbb{d}v}} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}0 \\1 \\{2v} \\{3v^{2}}\end{pmatrix}}}$ ${{where}\mspace{14mu}{Mz}} = {\begin{bmatrix}1 & 0 & 0 & 0 \\{- 3} & 3 & 0 & 0 \\3 & {- 6} & 3 & 0 \\{- 1} & 3 & {- 3} & 1\end{bmatrix}.}$
 10. The apparatus as in claim 8 wherein the secondpatch type comprises a Gregory patch having control vertices p₀₋₃,e₀₋₃+, e₀₋₃−, f₀₋₃+, and f₀₋₃−, wherein the Gregory patch is evaluatedin accordance with the following equations:${P\left( {u,v} \right)} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} G\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$ ${G = \begin{bmatrix}p_{0} & e_{0}^{-} & e_{3}^{+} & p_{3} \\e_{0}^{+} & F_{0} & F_{3} & e_{3}^{-} \\e_{1}^{-} & F_{1} & F_{2} & e_{2}^{+} \\p_{1} & e_{1}^{+} & e_{2}^{-} & p_{2}\end{bmatrix}},{where}$${F_{0} = \frac{{uf}_{0}^{+} + {vf}_{0}^{-}}{u + v}},{F_{1} = \frac{{\left( {1 - u} \right)f_{1}^{-}} + {vf}_{1}^{+}}{1 - u + v}},{F_{2} = \frac{{\left( {1 - u} \right)f_{2}^{+}} + {\left( {1 - v} \right)f_{2}^{-}}}{2 - u - v}},{F_{3} = \frac{{uf}_{3}^{-} + {\left( {1 - v} \right)f_{3}^{+}}}{1 + u - v}},$11. A method for ray tracing comprising: analyzing faces on asubdivision surface and responsively identifying the faces as being of afirst type or a second type, wherein a face is considered a first typeof face if it is a quad with all regular vertices, if none of its edgesor vertices are tagged as sharp, and if there are no hierarchical editsthat would influence the shape of a limit patch and wherein a face isconsidered to be a second type of face if it does not meet therequirements for being a first type of face; employing a first set ofprocessing techniques to faces of the first type to generate a firstpatch type and employing a second set of processing techniques to facesof the second type to generate a second patch type; and determining anintersection point between a ray and each of the patches of the firstpatch type and the second patch type.
 12. The method as in claim 11wherein the first patch type comprises a bi-cubic Bezier patch.
 13. Themethod as in claim 12 wherein a face of the first type includes a set ofcontrol vertices and wherein the first set of processing techniquescomprise extracting one ring of the control vertices around the face toform the bi-cubic Bezier patch.
 14. The method as in claim 12 whereinthe second patch type comprises a Gregory patch.
 15. The method as inclaim 14 wherein the second set of processing techniques for faces ofthe second type comprise iteratively refining the faces at each finersubdivision level, wherein when a maximum subdivision level is reached,a irregular face is approximated with the Gregory patch.
 16. The methodas in claim 11 wherein determining the intersection point between a rayand each of the patches of the first patch type and the second patchtype is performed using Newton's method.
 17. The method as in claim 16wherein to reduce the complexity of Newton's method, each patch of thefirst patch type and the second patch type are projected fromthree-dimensional space to two-dimensional space along the ray, with theray passing through an origin of the two-dimensional projection.
 18. Themethod as in claim 17 wherein finding the intersection point using thetwo-dimensional projection is accomplished by finding all of the (u, v)pairs such that P(u,v)=0, where 0≦u, v≦1 and where a Newton iterationcomprises: $\begin{bmatrix}u_{k + 1} \\v_{k + 1}\end{bmatrix} = {\begin{bmatrix}u_{k} \\v_{k}\end{bmatrix} - {\begin{bmatrix}\frac{\partial{P_{1}\left( {u,v} \right)}}{\partial u} & \frac{\partial{P_{1}\left( {u,v} \right)}}{\partial v} \\\frac{\partial{P_{2}\left( {u,v} \right)}}{\partial u} & \frac{\partial{P_{2}\left( {u,v} \right)}}{\partial v}\end{bmatrix}^{- 1}\begin{bmatrix}{P_{1}\left( {u_{k},v_{k}} \right)} \\{P_{2}\left( {u_{k},v_{k}} \right)}\end{bmatrix}}}$ where (u_(k),v_(k)) is the uv at step k, and(u_(k+1),v_(k+1)) is the uv at next step k+1.
 19. The method as in claim18 wherein the first patch type comprises a Bezier patch and wherein theBezier patch is evaluated in accordance with the following equations:${P\left( {u,v} \right)} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$${{\mathbb{d}{P\left( {u,v} \right)}}/{\mathbb{d}u}} = {\left( {0\mspace{14mu} 1\mspace{14mu} 2u\mspace{14mu} 3u^{2}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$${{\mathbb{d}{P\left( {u,v} \right)}}/{\mathbb{d}v}} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} P\mspace{14mu}{{Mz}^{T}\begin{pmatrix}0 \\1 \\{2v} \\{3v^{2}}\end{pmatrix}}}$ ${{where}\mspace{14mu}{Mz}} = {\begin{bmatrix}1 & 0 & 0 & 0 \\{- 3} & 3 & 0 & 0 \\3 & {- 6} & 3 & 0 \\{- 1} & 3 & {- 3} & 1\end{bmatrix}.}$
 20. The method as in claim 18 wherein the second patchtype comprises a Gregory patch having control vertices p₀₋₃, e₀₋₃+,e₀₋₃−, f₀₋₃+, and f₀₋₃−, wherein the Gregory patch is evaluated inaccordance with the following equations:${P\left( {u,v} \right)} = {\left( {1\mspace{14mu} u\mspace{14mu} u^{2}\mspace{14mu} u^{3}} \right){Mz}\mspace{14mu} G\mspace{14mu}{{Mz}^{T}\begin{pmatrix}1 \\v \\v^{2} \\v^{3}\end{pmatrix}}}$ ${G = \begin{bmatrix}p_{0} & e_{0}^{-} & e_{3}^{+} & p_{3} \\e_{0}^{+} & F_{0} & F_{3} & e_{3}^{-} \\e_{1}^{-} & F_{1} & F_{2} & e_{2}^{+} \\p_{1} & e_{1}^{+} & e_{2}^{-} & p_{2}\end{bmatrix}},{where}$${F_{0} = \frac{{uf}_{0}^{+} + {vf}_{0}^{-}}{u + v}},{F_{1} = \frac{{\left( {1 - u} \right)f_{1}^{-}} + {vf}_{1}^{+}}{1 - u + v}},{F_{2} = \frac{{\left( {1 - u} \right)f_{2}^{+}} + {\left( {1 - v} \right)f_{2}^{-}}}{2 - u - v}},{F_{3} = \frac{{uf}_{3}^{-} + {\left( {1 - v} \right)f_{3}^{+}}}{1 + u - v}},$